Production of a cellulose acylate resin film is largely classified to a solution film-forming method and a melt film-forming method. The solution film-forming method is a method in which a dope prepared by dissolving a cellulose acylate resin in a solvent is cast from a die onto a support, for example, a cooled drum to form a film. The melt film-forming method is a method in which a cellulose acylate resin is molten in an extruder and then extruded from a die onto a support, for example, a cooled drum to form a film. The cellulose acylate resin films formed by these methods are generally stretched in the lengthwise (longitudinal) direction and in the transverse (width) direction to develop in-plane retardation (Re) and retardation in the thickness direction (Rth). The stretched film is used as a phase difference film in a liquid crystal display element for the purpose of increasing viewing angles.
An example of the film-forming and stretching methods as described above is disclosed in Japanese Patent Laid-Open No. 2002-311240, wherein the irregularity in the angle in the direction of the slow axis is improved by reversing the direction of longitudinal stretching relative to the film-casting direction. Moreover, Japanese Patent Laid-Open No. 2003-315551 discloses a method for improving the orientation in the thickness direction (Rth) by stretching a film at a length-to-width ratio (L/W) of 0.3 to 2, wherein the length-to-width ratio means the value of the nip roll spacing used for stretching (L) divided by the width of a cellulose acylate resin film to be stretched (W).